My cannon rebel xt says error cf how do i fix it. was taking pictures took mycf card out to veiw on computer when i put it back it says err cf. tried different cf cards and it says the same thing. help

Step 1 Try to use a different CF card
Step 2. Remove the card and visually check the Compact Flash compartment on the camera.Use a flashlight and check the inside contacts (2 rows of thin golden pins). All the pins should be aligned & straight, and the Compact Flash compartment should be clean with no dirt or foreign objects inside.If you nottice some junk (stuff) in there you can try to remove it ( pull out the battery first) blowing some air (not canned air, only manual blower !) or pickup all the junk from inside with a toothpick or plastic tweezers.If you are NOT comfortable doing this, or have no experience in dealing with the very sensitive electronic parts, DO NOT TOUCH anything, just visually chect the inside and DO NOT try to remove the dirt (junk, stuff) mechanically, use just air.Use common sense and do it on your own risk ! You can damage your camera very easy ! If the pins are bended/broken/missing you have to send the camera out for service.
Step 3.Reset the system removing BOTH batteries !.You have to remove the small 3 volt memory backup cell to. It is a small round button cell battery located inside the
battery compartment.Leave the camera for 20-30 minutes with no battery, you can press the shutter button for few seconds to be sure all the power was consumed from the capacitors.Put back the battery , restart and see if it works.
If the error still occurs after following the steps above, your camera may need repair. Contact Canon’s technical support for further assistance.Due the fact is a 5 years+ camera you have to put in balance if is a good deal to send it out for repairs or to replace it.Good Luck.Let me know if worked.

Sounds like you didn't use the "safely remove hardware" function when you removed the card. You need to download the pics off the card and then format it in the camera to get it to work properly.